Acute Respiratory Alkalosis — FRCA Final MCQ

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EasyGeneral AnaesthesiaAcute Respiratory AlkalosisFRCA Final

A 35-year-old man (ASA I) is having an elective inguinal hernia repair under local anaesthesia. He becomes anxious and hyperventilates. His ABG shows: pH 7.58, PaCO2 2.8 kPa, PaO2 14 kPa, HCO3⁻ 24 mmol/L. What acid-base disturbance is present?

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Correct answer: A — Acute respiratory alkalosis

The ABG shows alkalotic pH (7.58) with low PaCO2 (2.8 kPa) and normal bicarbonate (24 mmol/L), indicating acute respiratory alkalosis from hyperventilation. In chronic respiratory alkalosis, renal compensation would have reduced HCO3⁻ (typically by 2 mmol/L per 1 kPa drop in PaCO2). The normal HCO3⁻ confirms this is acute. Clinical effects include lightheadedness, perioral tingling (from reduced ionised calcium due to increased protein binding in alkalosis), and reduced cerebral blood flow. Treatment: reassurance, slow breathing.

Reference: RCOA – 2023 – Final FRCA curriculum: acid-base physiology